It is conventional practice to use a solenoid operated directional valve which has a valve body with a mounting surface that embodies a standard hole or port pattern. The port pattern is triangular in shape and contains a pressure "P-port" at the apex of the triangle, a pair of tank "T-ports" at the base corners of the triangle, and a pair of line "A- and B-ports" in the opposite sides, respectively, of the triangle. By virtue of the standard port pattern the directional valve can be used readily in the hydraulic industry with hydraulic valve modules, various plates and manifolds and the like, all of which embody similar port patterns, to form compact and uniform sandwich and stack arrangements.
In solenoid operated directional valves of the foregoing character, the valve body frequently is formed by a casting operation in which cores are used to define the conventional annuli that are located in the bore that accommodates the spool and to define the ducts that lead to the annuli, and thereafter drilling operations are performed on the valve body to finish the bore and to connect the ports in the mounting surface to the appropriate ducts or annuli in the bore. It is also known to form the valve body from bar stock, or the like, and to perform the necessary drilling operations to form the bore for the spool with the appropriate annuli, and to connect the ports in the mounting surface to the appropriate annuli in the bore.
The valve bodies in these directional valves, whether formed from castings or bar stock, are known to create significant pressure drops in the fluids that flow through the various passageways. This characteristic of the valves creates problems which heretofore have been undesirable but which have been looked upon by the industry as inherent in this type of valve. Among the problems created are the necessity to supply the fluid to the valve at a higher pressure than is required at the work stations so as to accommodate the pressure drop and also to supply the fluid to the line ports at a pressure sufficiently high to meet the requirements at the associated work stations. The requirement for supplying fluid at the extra-high pressure to the P-port to accomodate the pressure drop creates various undesirable conditions, including the requirement that larger solenoids be used to move the spool than would otherwise be necessary, which in turn increases costs, may cause overheating problems, and the like.
A significant reason for the undesirable pressure drops that exist in the prior directional valves has been the existence of the standard port arrangement in the mounting surface of the valve body. Because of the requirement that the ports be located in a standard arrangement and size, the manufacturers have been severely limited in the design and location of the various passageways that must be fitted into the valve body. The valve bodies that are formed by casting operation can be cast while using special cores to define the core for the spool and the passageways which permit flow of fluid through the valve. However, the complexity of the casting prohibits passageways of ideal shape to be formed, and numerous other factors contribute to undesirable products or excessive costs, such as (1) cleaning requirements associated with castings, (2) porosity of the castings, (3) uncontrolled core shifting during casting operations, (4) finishing machining operations that must be made, (5) varying casting conditions caused by different hardnesses of the metal, and the like.
Prior valve bodies that have been machined from bar stock or the like have been free of some of the defects of cast valve bodies, but they have left much to be desired, primarily because the machining operations involved have caused some of the passageways in the valve body to be of a size and shape that inherently create undesirable fluid-flow conditions. This problem is particularly acute, because the annuli in the bore for the spool have widths substantially less than the diameter of the ports in the mounting surface, and therefore, when drilling from the ports to the annuli it is a common practice to use small diameter drill bits to avoid cutting the lands between the annuli. Thus, the end products, after the drilling operations have been completed include passageways of varying effective cross-sectional areas and sharp directional changes which produce undesirable pressure changes and resulting pressure drops.